The present invention relates to an ultraviolet/infrared absorbent green glass with a medium light transmittance. More particularly, the present invention relates to a glass having a greenish color shade and being suitable to be arranged next to a glass having a greenish color shade and a high visible light transmittance. The present invention also relates to a glass having a medium visible light transmittance, a low solar energy transmittance, and a low ultraviolet transmittance, so that it is useful for a privacy protecting glass of a vehicle.
Recently, a variety of glasses with ultraviolet/infrared absorptivity to be used as a vehicle windshield have been proposed from a viewpoint of preventing degradation of luxurious interior materials and reducing cooling load of the vehicle.
A front windshield of a vehicle needs to have a visible light transmittance higher than a specific level to secure enough visibility for a driver. An ultraviolet and heat rays absorbent glass mounted in the windshield has a greenish color shade because the glass also absorbs visible light having a wavelength near the ultraviolet range and the infrared range.
A glass for a rear window of a vehicle has no need such as that of the front windshield, and a glass with a relatively low visible light transmittance is preferably used for a rear windshield of a vehicle in a viewpoint of privacy protection. A glass having almost neutral color such as grayish color shade and a low visible light transmittance has been used.
A colored glass disclosed in WO 93/07095 consists of soda-lime-silica glass including colorants consisting of 0.45 to 2.5 weight percent of Fe2O3 (total iron), 0.001 to 0.02 weight percent of CoO, 0 to 0.0025 weight percent of Se, and 0 to 0.1 weight percent of Cr2O3. The solar energy transmittance (TG) of the glass is lower than the luminous transmittance measured by C.I.E. illuminant A (TLA). The glass with a thickness of 3.85 mm has a solar energy transmittance in a range of 10 to 48 percent and a luminous transmittance in a range of 20 to 60 percent.
A dull gray or green colored heat ray absorbent glass with a low light transmittance disclosed in WO 95/18075 consists of soda-lime-silica glass including colorants consisting of 0.90 to 1.90 weight percent of Fe2O3 (total iron), 0.002 to 0.25 weight percent of CoO, 0.0010 to 0.0060 weight percent of Se, and 0.1 to 0.2 weight percent of TiO2. The glass with a thickness of 4 mm has a luminous transmittance in a range from 10.0 to 60.0% measured by using C.I.E illuminant A, an ultraviolet transmittance of less than 25.0%, an infrared transmittance of less than 50.0%, a dominant wavelength in a range from 480 to 575.5 nanometers by C.I.E. illuminant C, and an excitation purity of less than 6.0%.
A colored glass disclosed in WO 97/30948 consists of soda-lime-silica glass including colorants consisting of 1 to 3 weight percent of Fe2O3 (total iron), 0.1 to 1.0 weight percent of TiO2, 0 to 500 ppm Co3O4, and FeO in a range from 10% to about 37%. The glass with a thickness of 4 mm has a visible light transmittance in a range from 10% to about 70% measured by C.I.E illuminant A.
A soda-lime-silica glass disclosed in WO 94/18135 has a neutral color by colorants including primary iron given by the following equation:FeO (wt. %)≧0.007+(an optical concentration−0.036)/2.3 Also, the colorants include 0.25 to 1.75 weight percent of Fe2O3 and at least one selected from a group consisting of Se, CO3O4, Nd2O3, NiO, MnO, V2O5, CeO2, TiO2, CuO, and SnO. The glass with a thickness of 4 mm exhibits a luminous transmittance of more than 32%, an ultraviolet transmittance of less than 25%, a solar energy transmittance at least 7% less than the luminous transmittance, and a dominant wavelength preferably at less than 570 nanometer. Certain embodiments thereof may be used as a privacy protection glass.
The colored glass disclosed in WO 93/07095 includes Fe2O3, CoO and Se, and/or Cr2O3 is added thereto. Examples in PCT 6-503300 exhibit that Se is added to reduce the excitation purity, thereby being able to harmonize with a glass having a brighter green color shade. However, a large quantity of Se is not preferable in terms of the environmental consideration because Se has toxicity and is easy to vaporize. Cr2O3 sometimes forms chromite stones in the melting process and fluxes into a product to cause a defect. As chrome with an octahedral coordination has toxicity and is harmful to the environment, it is not preferable to be added to the glass as well.
A dull grayish green colored heat ray absorbent glass with a low light transmittance disclosed in WO 95/18075, which includes 0.1 to 2.0 weight percent of TiO2 as an essential component, is not preferable because TiO2 is expensive ingredient, thereby increasing the batch cost. Besides, the glass does not match well to a brighter green colored glass when arranged adjacently each other because of dull grayish green color shade.
Since the glass composition disclosed in WO 97/30948 also includes TiO2 in a range from 0.1 to 1.0 weight percent as an essential component, the batch cost increases unfavorably.
The glasses having a medium visible light transmittance among the glasses disclosed in WO 94/18135 are provided with a halftone color shade due to colorants such as Fe, Ni, Se, Co, in the components. All of the samples include a large amount of Se, which is not favorable. Among them, the glass including Fe of more than 1.0 weight percent is not suitable for a windshield of a vehicle in a view of safety since the sample with a thickness of 4 mm has a visible light transmittance of less than 40% and has too dark shade. The glass has a dull grayish green color, thus it does not match to a brighter green colored glass when arranged next to each other.
Though the aforementioned glass with a low visible light transmittance is superior in terms of the privacy protection, an occupant in a vehicle cabin can not see the outside clearly through the glass. In a case that a high mounted breaking lamp is employed in a cabin of a vehicle, the glass having a low visible light transmittance is not suitable for a rear window because of its poor visibility. On the other hand, a glass with a medium light transmittance can be sufficient to some extent for both privacy protection and safety.